Anna's paid back $6,000 in a year

Using hidden cameras, the ABC filmed on two occasions when Anna handed back hundreds of dollars of her pay.

At one handover, her boss can be seen accepting $150 in cash from Anna in the manager's office of the Brisbane store.

She said she hands back about $11 for every hour she works.

"The government pay is $25 per hour for casual staff. What I get is $14 per hour. Every week I pay [back], because they pay me every week," she said.

"[I] take the cash out of the ATM, and hand it back."

Anna showed the ABC her bank statements detailing her withdrawals, saying she had paid back more than $6,000 since the start of this year.

Cash back scam concerns raised previously with 7-Eleven

Systemic wage fraud and the underpayment of workers was exposed by Four Corners and Fairfax Media last year, prompting the company to set up a wages compensation panel headed by former Australian Competition and Consumer Commission chairman Allan Fels.

A spokesman for the company told the ABC that 7-Eleven "takes any allegation of illegal activity in our franchisee network extremely seriously".

"We are not aware of any allegations relating to this store, and no staff members have raised any concerns with us. As soon as the allegations were raised with us we commenced an internal investigation," the spokesman said.

He said 7-Eleven will act upon any allegations of illegal activity, "up to and including termination of the Franchise Agreement".

In response to questions from the ABC, a spokesman for the Fair Work Ombudsman said any employer who tells a worker that they have to pay part of their wages back is breaching work laws.

"The Fair Work Ombudsman is concerned about the use of 'cash-back' arrangements we are seeing in some 7-Eleven cases," he said.

In June, another 7-Eleven franchisee was fined more than $400,000 over a cash back scheme.

It is the largest court-imposed penalty achieved by the Fair Work Ombudsman, whose investigation found that the franchisee had stripped back $82,000 from 12 of his employees, some of whom were international students.